Typically, containers such as sumps are placed beneath fluid conduit systems to contain fluids which may leak from the systems. For example, gasoline service stations usually include an underground fueling network of dispenser sumps, fuel conduits and entry fittings. Such sumps usually comprise a plastic or metal shell which is buried in backfill and/or cement such that the mouth of the sump is open to air at the level of the surface. The sumps are used to capture gasoline which may leak from fuel conduits and dispensers located above the sump. Containment of such leakage prevents gasoline from contaminating the ground and ground water. To prevent leaked fluid from seeping back out of the sump, entry fittings are used at locations where pipes enter the sump. These fittings also prevent the flow of ground water into the sump. In order to maintain a tight seal between the sump wall and the entry fitting, the wall must be sufficiently flat and free from irregularities. After the sump captures leaked fuel, a liquid removal apparatus can be inserted into the sump to remove the fuel.
In addition to serving to capture leaked fuel, sumps also serve to provide access to the fuel pipes and associated couplings of the fuel system. After installation of the sump, individuals may enter the sump to maintain fuel and entry fittings. Thus, the sump must be sufficiently rigid to maintain shape integrity despite the backfill surrounding the sump and the weight of the individuals who may enter it.
While many advancements have been made in the field of underground sumps, a number of problems still exist. Among the problems experienced with such containers is their tendency to deform under the weight of the backfill and/or maintenance personnel. Such deformations can result in the rupturing of the sump, thereby creating the risk that fuel will be emitted into the surrounding environment. Furthermore, deformations of the sump can jeopardize the integrity of the entry fitting seals, again creating the risk of contamination to the environment.
Another problem experienced by manufacturers of such sumps is the difficulty in manufacturing a sump with walls sufficiently flat to maintain a tight seal between the entry fitting and the sump. Rotational molding processes are commonly used to manufacture sumps. A rotational molding process involves inserting powdered plastic into a rotating mold. During the rotation, the powdered plastic becomes heated and takes on the shape of the mold. When allowed to cool, the plastic hardens thereby creating the sump defined by the mold. Although this process has been found to be highly efficient and inexpensive, it is not without disadvantages. Unfortunately, the process often results in undesirable variations in the thickness and shape of the sump walls and the formation of irregularities on sump surfaces. These problems are believed to occur during the cooling of the plastic. Due to these disadvantages, it is often difficult to maintain a sealing relationship between an entry fitting and the wall of a sump formed by this process.
Consequently, despite significant work undertaken in the industry and the ongoing problems with sump deformation and leakage, heretofore there has not been provided a relatively inexpensive sump that can withstand large compressive forces and provides tight sealing of entry fittings.